Oscillator controlled relay system



y 3, 1951 w. H. WANNAMAKER, JR 2,559,266

OSCILLATOR CONTROLLED RELAY SYSTEM Original Filed June 22, 1944 2Sheets-Sheet 1 FIG. I

FIG. 3

R ELAY CURRENT VANE POSITION INVENTOR. WILLIAM H.WANNAMAKER JR.

ATTORNEY.

y 3, 1951 w. H. WANNAMAKER, JR 2,559,266

OSCILLATOR CONTROLLED RELAY SYSTEM Original Filed June 22, 1944 2Sheets-Sheet 2 FIG.6

INVENTOR. WILLIAM H. WANNAMAKER JR. BY a g ATTORNEY.

Patented July 3, 1951 e OSCILLATOR CONTROLLED RELAY SYSTEM William H.Wannamak er, Jr., Flourtown, Pa., as-

signor to Minneapolis floneywell Regulator Company, Delaware Originalapplication 'Juiieff'zz, 1944,

Minneapolis, Minn a corporation of seal No.

541,575. Divided and this application July 9, 1943, Serial No. 103,842

I A primary object of the present invention is to provide an improvedcontrol system of the type in which control actions are effected throughelement on a small change in the value of the controlling quantity orcondition.

This application is a division of my prior application Serial No.541,575, filed June 22, 1944, for control apparatus, which issued asPatent No. 2,531,313, on November 21, 1950, and relates specifically tothose forms of the invention disclosed in said prior application invwhich three position'control is obtained with apparatus including oneelectronic valve adapted to operate as an oscillator, or not so tooperate, accordingly as an inductive reactance included in the apparatusis varied by the adjustment of a control element in predeterminedresponse to variations in'the controlling quantity or condition, andalso including one or two other electronic valves.

The various features of novelty which characterize the invention claimedherein are pointed out with particularity in the claims annexed to andforming a part of this specification. For a better understanding of theinvention, however, its advantages, and specific objects attained by itsuse, reference should be had to the accompanying drawings anddescriptive matter in which I have illustrated and described preferredembodiments of the invention.

Of the drawings:

Fig. 1 is a diagram showing a circuit arrangement adapted for use in athree position control system;

Fig. 2 is a diagrammatic view, taken at right angles to Fig. 1, of thecontrol coils and vane of Fig. 1;

Fig. 3 is a diagram illustrating plate current variations produced inthe operation of the apparatus shown in Fig. 1;

Fig. 4 is a diagram showing a modification of the electromagnetic switcharrangement shown in Fig.1; and

Figs. 5 and 6 are diagrams illustrating different modifications of thethree tem shown in Fig. 1.

In Fig. l, I have diagrammatically illustrated a simple embodiment of myinvention comprising an electronic tube A which does or does not 9Claims. (01. 175-320) position control 'sysoperateas an oscillator,depending on the mutual inductance of suitably disposed inductance coilsB, b, B and b. The mutual inductance of said coils depends upon theposition of an inductance 5' shield 01'' vane C movable into and out ofa position in which it is directly interposed between 'thecoils- Theshieldv or vane C is formed of sheet metal such as aluminum, copper orbrass of good electrical conductivity, and changes in its positionrelativeto. the coils B, b, B and b vary their mutual inductance in aknown manner.' The shield or vane C is shown as carried byan arm H whichmay be the deflecting ele-' ment of a milliv'oltmeter, not shown, whichde- 'fiects in response to variationsin the voltage of r a thermocoupleas the temperature of the latter varies, or which deflects in responseto the deflection of some other control instrument of device. V Theelectronic tube A shown in Fig. 1, is a rectifier-beam power amplifiertube of the type and-term commonly known as the 117N7GT tube, andcomprises a tetr'ode valveor section a and a diode valve or section a.-The use-of that particular tube is not essential to the practice of thepresent invention. I consider it desir-able, if not essential, however,toemploy a tube enclosing a..tetrode or other multi-grid elec tronicvalve a having a screen gridas well as a control grid," .The screen gridacts as a shield between the anode and control grid elements of thevalve 'a for decreasing the capacitance between those elements,so thatthe tendency of the valve to oscillate due to inherent control grid toanode capacitance is eliminated or at least minimized. As'a result,starting and stopping of the oscillations of the valve 1 are determinedsolely. by the relative positions of the vane C and the coils B, b B'and b. In addition, the screen grid permitsoperation of the valve a at ahigher frequency than would otherwise be possible because its useeliminates or minimizes the tendency of the inherent control grid toanode capacitance to maintain oscillations regardless of the position-ofthe vane C. Oscillation 01' the valve a at such higher frequency isdesirable because a given change in mutualinductance between the controlcoils B, b, B, and b then produces a'greater change in the amplitude ofoscillation. In consequence, the screen grid contributes to thesharpness or sensitivity of the response of'the valve 'a to "movement ofthe vane in the range of its movement in which oscillation of the valvea is initiated and interrupted.

As shown in'Fig. 1, the valve a, which is energized by alternatingcurrent supply conductors I and 2, comprises a cathode 3 with beam plateextensions 3a, control grid 4, screen grid 5, plate or anode 6 andcathode heating filament I. The terminals of the filament l areconnected to the supply conductors I and 2 by conductors 8 and 9,respectively.

The diode a comprises an anode or plate 3| connected to the supplyconductor 2 by the conduotor 9 and a cathode 30 connected to the supplyconductor I by a condenser 52. The connected terminals of the cathode 30and the condenser 52 are connected to the anode 6 of the valve a by aconductor 50, a portion of a conductor I8, a choke coil I and a portionof a conductor II. As shown, the choke coil I0 is surrounded by a shieldIA. The cathode 3 of the valve a is connected to one terminal of a relaycoil D. The second terminal of the coil D is connected to one terminalof a relay coil DA. The second terminal of the coil DA is connected by aconductor I00 to the supply conductor 2. The coils D and DA are shuntedby condensers 32 and 33, respectively, and the coil DA is also shuntedby a resistor IOI. The inductance coils B and b are coaxial and areseparated by a kerf-like space into and out of which the vane moves asthe arm H deflects. The

inductance coils B and b are similarly coaxial and are latterlydisplaced from the coils B and b as shown in Figs. 1 and 2 and arespaced apart to provide an extension of the kerf-like space between thecoils B and b. In its position shown in Figs. 1 and 2, the vane C isdirectly interposed between the coils B and b and reduces the mutualinductance of those coils. A deflection of the vane C to the right fromits position shown in Figs. 1 and 2 will minimize or eliminate theeffect of the vane C on the mutual inductance of the coils B and b. By asuitable deflection to the left from its position shown in Figs. 1 and2, the vane C may be adjusted into a position in which it will minimizeor eliminate the mutual inductance of the coils B and b as well as themutual inductance of the coils B and b. In its position shown in Figs. 1and 2, the vane C does not significantly affect the mutual inductance ofthe coils B and b.

As shown, one terminal of the coil B is connected to the anode 6 of thevalve a by a condenser I3 and the previously mentioned conductor II. Thesecond terminal of the coil B is connected to one terminal of the coilB, and the second terminal of the coil 13' is connected to ground byconductor I4. One terminal of the coil b is connected to the controlgrid of the valve (1 by a condenser I and a conductor I6. The secondterminal of the coil b is connected to one terminal of the coil b andthe second terminal of the coil 2) is connected to the ground connectionI4. A high resistance i'I connects the connected terminals of thecontrol grid 4 and condenser I5 to the connected terminals of thecathode 3 and the relay coil D. The last mentioned terminals areconnected through a condenser 20 to ground at the point 2I. The capacityof the condenser 20 is so chosen that in conjunction with the groundedconductors, the condenser forms a low impedance connection for highfrequency current flow between the cathode of the valve a and theinductance coils B, b, B and b. A condenser I9 connects the connectedterminals of the cathode 3 and relay coil D to the end of the choke coilI0 connected to the conductor I8. The latter connects the choke coil Illand condenser I9 to the screen grid 5.

Ample voltage for energizing the series connected coils D and DA isinsured, as is hereinafter explained, by connecting the diode anode 3Iand grid valve cathode 3 to the supply con ductor 2, and by connectingthe diode cathode 30 and the anode 6 of the valve a to the supplyconductor I as previously described. In the contemplated operation ofthe apparatus shown in Fig. l, the current flow through the relay coilsD and DA will be too small to energize either relay coil when the vane Cis in its right hand or low position in which the vane does notsignificantly reduce the mutual inductance of either pair of controlcoils, and the valve a then oscillates with a relative high frequency.On movement of the vane C into its intermediate or neutral" position inwhich it substantially minimizes or eliminates the mutual inductance ofthe coils B and 1) without significantly min imizing the mutualinductance of the coils B and b. the amplitude of oscillation of thevalve 11 is reduced and the current flow through the valve a and relaysD and DA increases sufliciently to operatively energize the relay D butis still too low to operatively energize the less sensitive relay DA.When the relay D is thus energized its associated armature switchelement D is moved out of the position in which it connects the controlterminals 23 and 25 and into the position in which it connects theterminals 24 and 23.

When the vane C moves to the left from its position shown in Fig. 1 intothe position in which it substantially minimizes or eliminates themutual inductance of the control coils B and b as well as of the coils Band b. the oscillation of the valve is interrupted and the current flowthrough the coils D and DA is so increased that the relay DA isoperatively energized. In consequence, the armature switch element D isthen raised to disconnect the terminals 23' and 25' and to connect theterminals 24' and 23. On a reverse movement of the vane from its lefthand or high position into its neutral position shown in Fig. 1, therelay energizing current is sufficiently reduced to deenergize the relaycoil DA without deenergizing the coil D, and the armature D then dropsback into engagement with the terminal 25. Movement of the vane C to theright of its position shown in Fig. 1 so deenergizes the coil D that thearmature D drops into engagement with the terminal 25.

The variations in the relay current produced by the adjustment of thevane C of Fig. 1 into its three different positions as just describedare illustrated diagrammatically in Fig. 3 wherein the horizontal curvesections 2'', i and F represent the low, intcrmediatc" and high" valuesof the relay current maintained when the portion of the vane C is suchthat it respectively (1) does not significantly reduce the mutualinductance of either pair of control coils, (2) substantially eliminatesthe mutual inductance of one pair of control coils only, and (3)substantially eliminates the mutual inductance of both pairs of controlcoils. The inclined curved portions connecting the portions 1'', i andconnecting the portions 1' and 2' illustrate the relatively abruptcharacter of the current variations produced as the vane moves in eitherdirection into or out of its intermediate position; As will be apparent,the length of the intermediate portion of the curve may be increased ordecreased by varying the displacement of the coils B and b from thecoils B and b. This means of course that thepositions of the two sets ofcontrol coils should be determined with proper regard to thecontemplated range of movement given the vane C.

The armature switches D and D and associated terminals 23, 24, 25, 23',24 and 25' may be associated with control apparatus of a known type tosupply heating current or fuel to a furnace at one rate when both ofcoils D and DA are deenergized, at a second rate when the coil D isenergized and coil DA is deenergized, and at a third rate when the coilsD and DA are both energized. In many cases the supply of heating currentor fuel may'be entirely cut off when the vane is in its high position.As will be readily understood, the apparatus shown in Fig. 1 may be usedto provide three-position control for other purposes than furnaceregulation.

With a control system of the type shown in Fig. l, the two separaterelay units may be replaced by a single relay DE in which the 00115 Dand DA are rigidly connected end to end in an instrument relay structureof a type and form illustrated and described in my parent applicationSerial No. 541,575. In the relay DE, the coils D and DA of Fig. 1 actadditively on a common armature D associated with control contacts asshown diagrammatically in Fig. 4. In Fig. 4 three spring contact fingersD, D and D are arranged side by side but out of contact with one anotherwhen the armature D is in its idle position shown in Fig. 4. Whenactuated, the armature D turns counter-clockwise and moves its contact Dinto engagement with the contact finger D When used in the controlsystem shown in Fig. 1, the armature D of Fig. 4 may be actuated by aforce which is just suflicient to move contact D into engagement withthe contact arm D when the vane C is in its low position, which issufllcient to move the contact arm D into engagement with the contactarm D when the vane C occupies its neutral position, and which issufllcient to move the contact D into engagement with the contact D whenthe vane C moves into its high position. Contact member adjustmentswhich are the reverse of those just described will be produced bymovement of the van C from its high position into its low position.

The small current normally flowing in the windings when the vane is inits "low position moves the contact member D into engagement with thecontact D" andgthereby enables the control apparatus .to effect theappropriate low control action. The contact D thus serves to preventunsafe operation as a result of tub failure orother accidentalinterruption of all current flow through the winding of the relay unitDE. The'control circuit conductors associated with the contacts D, D", Dand D, to effect appropriate low, neutral and high control actionsaccording to the position of the vane C, may be arranged in any ofvarious suitable ways as those skilled in the art will understand.

With the cathode 5 of valve a and anode 3| of valve 11' connected to thesupply conductor i and with the anode Ii of valve a and cathode 55 ofthe valve a' connected to the supply conductor I through the condenser52 as shown in Fig. 1, the

eifective energizing voltage impressed on the series connected relaycoils D and DA is approximately double the line, or supply, voltagebetween conductors I and 2. During periods in which the valve a is notoscillating and the coils D and DA may be effectively energized, thecondenser 52 is discharged by the valve a during the half cycles whichalternate with half cycles in which the condenser is charged by thevalve a. Durin each half cycle in which the valve a is conductive and isbuilding up a charge on the condenser 52, the valve a is not conductiveand does not interfere with the condenser charging operation. Inconsequence, the eilective voltage impressed on the series connectedrelay coils D and DA in the following half cycle in which valve a isconductive is the sum of the voltage between the supply conductors I and2 and the approximately equal condenser potential.

When the valve a is oscillating it is not operative to effectivelydischarge the condenser 52, and

after the condenser is fully charged by the diode valve a, the latterceases to pass any significant amount of current since the potential ofthe condenser 52 is then approximately as high as the opposing linevoltage durin the half cycles in which the diode can conduct current.The current flow through the relay coils due to the sixty cycleunidirectional voltage pulses impressed on them is smoothed out by theassociated condensers 32 and 33 so that the relays operate substantiallyas they would if they were energized with continuous unidirectionalcurrent. The general combination of a condenser, diode, grid valve andload device, as shown in Fig. 1, is not claimed herein but is claimed inmy copending application Serial No. 541,576, filed June 22, 1944, whichissued as Patent No. 2,514,918 on July 11, 1950.

In Fig. 5, I have illustrated an arrangement in which two electronictubes A and A and three electromagnetic relays, D D and D are employedto effect three-position control in response to variations in the mutualinductance of a single pair of control coils B and b. The winding of therelay D is connected in series with the filament elements of the tubes Aand A and a conductor I III between the branch conductor 8 from thesupply conductor I and a branch conductor I05 from th supply conductor2.

In Fig. 5, the valve a of the tube A and control coils B and b areassociated by circuit provisions similar to those shown in Fig. 1,except that in Fig. 5 the choke coil I0 is connected to the screen grid5 by a variable resistance III. The winding of the relay D is connectedbetween the choke coil III and the conductor 2. In Fig. 5, the oathodeis directly connected to the supply conduotor I, and the plate 3| oflthe diode is connected by a conductor I06 and a resistance III! to oneterminal of a potentiometer resistance I08. The latter has its secondterminal connected to the supply conductor 2 through the conductor 34which is connected to one terminal of the relay D".

The valve A may be a beam power amplifier tube of the 35L6-GT form,comprising cathode,

control grid, screen grid and plate elements 5, I, 5 and 6,respectively, similar to those of the valve (1 included in the tube A.The cathode 5 of the tube A" is connected to the resistance "I at anadjustable intermediate point through anadjustable contact I09. Theplate 6 of the tube A" is connected to the screen grid 5 of the tube andis connected by a conductor III) to one terminal of the relay D Thesecond terminal of that relay is connected to the previously mentionedcondoctor I. The control grid 4 of the tube A" is connected through asliding contact III to an intermediate point along the length of apotentiometer resistance H2. The latter is connected in parallel withthe windin of the relay D and the by-pass condenser H which connects theterminals of that relay.

The terminals of the resistance I0'I are connected by filter condensersH4 and H5 to the conductor 34 and thereby to the supply conductor 2. Thecondensers H4 and H5 may each have a capacitance of about 8 mid. Thecapacitance of the condenser H3, and of the bypass condenser IIGconnecting the terminals of the relay D", may be about 2 mfd. As shown,the screen grid 5 of the tube A is connected to the choke coil I0through the variable resistance III, which may have a value of the orderof onequarter of a megohm. The resistances I01, I00 and H2 may well beabout 1,000 ohms, 200 ohms and 50,000 ohms, respectively. The resistanceand capacitance values just stated are given by way of illustration andexample and are not critical. It is practically desirable, however, thatthe resistance I08 should be low, as this prevents the tube A from beingappreciably self biased. By the adjustment of the amount of theresistance H1 in circuit, it is possible to vary the upper limit of theneutral range of variation in value of the controlling quantity which byits variations varies the position of the vane 0 relative to the coils Band b.

As shown, the energization of the relay D adjusts a movable contact Dinto engagement with a stationary front contact. The energization of therelay D moves contacts D and D out of engagement with stationary backcontacts and moves a contact D into engagement with a correspondingstationary front contact. The energization of the relay D moves contactsD" and D out of engagement with associated stationary back contacts andmoves contact D into engagement with a stationary front contact.

In the contemplated operation of the control system shown in Fig. 5 theenergization of the filament circuit of the tubes A and A energizes therelay D and thereby connects the relay contact D to an energizingcurrent terminal EC. The latter is then connected through the contact Dand one or more other relay contacts to high, neutral or low controlconductor terminals EH, EN and EL, respectively, depending upon theposition of the vane C relative to the control coils B and b. Thus whenthe vane C is displaced to the left out of operative relation to thecoils B and b as a result of the "low value of the controlling quantityor condition, the valve a in the tube A oscillates and its space currenthas its minimum value. In consequence, the potential then impressedthrough the resistance H2 and contact III on the control grid 4 of thetube A permits the potential across the resistance I08 to give thecontrol grid of the tube A a positive bias. In consequence, the currentflow then maintained through the tube A is large enough to energize therelay D and the latter operates to connect the conductor EC through therelay contacts D", D and D to the low" control conductor terminal EL.

As the value of the controlling quantity or condition increases andmoves the vane C into position to reduce the mutual inductance of thecoils B and b, the oscillation of the valve a in the tube A decreases.The resultant increase in the space current of that valve eliminates thepositive bias on the control grid 4 of the tube A and therebydeenergizes the relay D On the deenergization of the relay D theenergizing terminal EC is connected through the relay con- 8 tacts D", Dand D" to the neutral control terminal EN.

On a further increase in the value of the control quantity or conditionand the resultant movement of the vane C and reduction in the mutualinductance of the coils B and b, the oscillation of the valve a of thetube A is further reduced and the space current of that valve is furtherincreased to the value required to energize the relay D". Theenergization of the relay D operates to connect the energizing terminalEC to the high control terminal EH through the relay contacts D D and DWith the arrangement shown in Fig. 5, the value of the controllingquantity or condition at the low value end of its neutral range may beincreased or decreased by adjusting the contact I09 to the left or tothe right, respectively, along the resistance I08, so as to increase ordecrease the value of the plate current of the valve A maintained at agiven value of the plate current of the valve a of the tube A. Ingeneral, the adjustment of the contact I09 should be accompanied by acorresponding adjustment in the same direction of the contact I I Ialong the resistance H2. The use of the potentiometer resistances I08and I I2 connected in bridging relation to the supply conductorsminimizes the effect of variations in the supply voltage on the controlactions effected. As previously stated, when the adjustable resistanceH1 is employed as shown in Fig. 5, it serves by its adjustment to varythe value of the controlling quantity or condition at the upper end ofthe neutral range of that value.

Fig. 6 illustrates a modification of the threeposition control system ofFig. 5. I now deem this modification preferable to the arrangement ofFig. 5 because its use makes possible a substantial reduction in thenumber of circuit components which is required.

The three position control system of Fig. 6 includes two electronictubes A and A both of which may be of the beam power amplifier type suchas the 35L6-GT tube, and two electromagnetic relays D and DA. Relay D isconnected in the output circuit of the tube A and relay DA is connectedin the output circuit of the tube A The output circuits of tubes A and Aare connected in inverse manner to the alternating current supplyconductors I and 2 so that tube A is conductive during half cyclesalternating with those during which tube A is conductive. As isexplained hereafter, the conductivity of tube A is controlled inaccordance with that of tube A In Fig. 6, the tube A is associated withthe two control coils B and b in such manner that the oscillation oftube A is initiated and/or interrupted by movement of the vane C out ofor into the position in which it is directly interposed between thecoils B and b. The output circuit of tube A may be traced from thesupply conductor I to the cathode 3, the anode 6, a choke coil I0shunted by a resistance 51 and the winding of relay D to the supplyconductors 2. When tube A is oscillating its conductivity is too smallto permit flow in the said output circuit of sufficient plate current toenergize relay D. When the oscillation is interrupted sufficient platecurrent to energize relay D flows in the output circuit.

As noted above, the conductivity of the tube A is controlled inaccordance with the conductivity of the tube A This result is producedby impressing on the input circuit of tube A a voltage produced by theflow of plate current through the winding of relay D. To this end thecathode 3 of tube A is connected to one end of the winding of relay Dand the control electrode 4 is connected to the other end in such mannerthat the flow of current through the said winding produces a negativepotential on the control electrode 4. This potential is held over to thehalf cycle during which the tube A is conductive by the condenser II3.The magnitude of this potential varies in accordance with the platecurrent flow through the winding of relay D, and therefore, inaccordance with the condition of oscillation of tube A Hence, theconductivity of tube A is varied in accordance with the lattercondition. The output circuit of tube A may be traced from the supplyconductor I through the Winding of relay DA shunted by condenser Hi tothe plate 6 and the cathode 3 of tube A to the supply conductor 2.

According to the contemplated operation of the control system of Fig. 6,insuflicient plate' current flows through tube A to energize relay Dwhen the vane C is out of the position between coils B and b and tube Ais oscillating. Such small value of plate current as then flows 10 trolcoils B and b relative to one another and to the cooperatingvane C. Thestabilizing effect of the resistance 53 is attributable in large part atleast to the fact that it minimizes the effect of the capacitance of theconductor connections to the control coils B and b.

The control apparatus shown diagrammatically in Figs. 1, 5 and 6 ischaracterized by its inherent simplicity, reliability and capacity foroperation with high sensitivity. By way of example, and not by way oflimitation, it is noted that in one practical embodiment of the controlapparatus illustrated in Figs. 1,5 and 6, the capacitances of thecondensers I3 and I5 are 0.00005 and 0.00007 mfd., respectively; and thecapacitance of each of .the condensers I9 and 20 is 0.0001 mi'd., thoughthe capacitance value of neither is critical. The capacitances of thecondensers I3 and IS with the capacitance of the oscillator \alve andthe distributed capacitances of the circuit elements provide thecapacitance in the series resonant circuit porthrough the winding ofrelay D is efiective to produce only a small negative potential on thecontrol electrode of tube A and consequently, the latter is then fullyconductive and relay DA is energized. Under this condition the armatureD of relay D will be in engagement with its back contact, shown as thelower contact, and the armature of relay DA will be in engagement withits front or upper contact. As the vane C deflects into an intermediateposition between the coils B and b, the magnitude of oscillation of tubeA decreases and its plate current increases sufliciently to produce apotential drop across the Winding of relay D of the required magnitudeto effect deenergization of relay DA by decreasing the conductivity oftube A but not enough .to energize relay D. The armatures of both relayswill then be in engagement with their lower contacts. Upon furtherdeflection of vane C toward the position directly between the coils Band b, the plate current of tube A increases to a value suflicient toenergize relay D. Such additional increase in plate current produces nochange in the operative condition of relay DA, and hence, the armature Dof relay DA will then remain in its lower position while the armature ofrelay D is adjusted to its upper position.

In Fig. 6, the terminals of the coils B and b respectively connected tothe condensers I3 and i5 are connected by a resistor 53 which isemployed to insure substantially complete stability of the oscillatorsystem and to prevent positively the valve A from oscillating when theram C is in position to reduce the mutual inductance of the controlcoils to a minimum. I have experimentally determined that thesensitivity of the response of a control system including a resistor 53arranged in the manner shown in Fig. 6v to movement of the vane C is noteffected by the use of the resistor 53, if the resistance of the latteris above 10,000 ohms. While the use of the resistor 53 in the controlapparatus shown in Fig. 6 is not imperative, it is advantageous and hasthe practical advantage of increasing the permissible mechanicaltolerances in respect to the spacing of the two contions of the system.The condensers I3 and I5 also serve as blocking condensers preventingrisk of injurious current flow through coils B and b. due to the normal60 cycle. -120 volt potential between the supply conductors I and 2. Thecondensers I9 and 20 serve as by-pass condensers and their respectivecapacitances are not critical, as noted above.

Novel features of the apparatus disclosed, but not claimed, herein areclaimed in my said application Serial No. 541,575 and in the divisionsthereof, Serial No. 607,034 filed July 25, 1945, now Patent No.2,511,608 of June 13, 1950, and Serial No. 634,599 filed December 12,1945, now Patent No. 2,511,819 of June 13, 1950.

While, in accordance with the provisions of the statutes, I haveillustrated and described the best forms of my invention now known tome, it will be apparent to those skilled in the art that changes in theform of the embodiments of my invention illustrated and described hereinmay be made without departing from the spirit of the invention as setforth in the appended claims. It will be understood also that use maysometimes be advantageously made of some features of my inventionwithout a corresponding use of other features.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent, is:

1. Control apparatus comprising a control device including an electronicvalve having an input electrode included in an input circuit, an outputelectrode included in an output circuit, and a common electrode commonto both of said circuits, a load circuit including said outputelectrode, an impedance device connected in a feedback circuit betweensaid input and output circuits to form an oscillator circuit, saidfeedback circuit being operative to feed back electrical energy fromsaid output circuit to said input circuit under the control of saidimpedance device, adjustable means operable to vary the impedance ofsaid impedance device between first, second, and third values at whichsaid feedback circuit is operative to cause oscillation of saidoscillator circuit at maximum, intermediate, and minimum amplitudes,respectively, and a bias impedance included in said input circuit andoperative to vary the conductivity of said load circuit in accordancewith the amplitude of oscillation of said oscillator circuit and hencein accordance with the adjustment of said imped- 11 ance device, a relaydevice having a first operating portion, a second operating portion, andcontact means jointly controlled by said operating portions and havingfirst, second, and third operating positions, the position assumed bysaid contact means being dependent upon the selective operativeenergization of said operating portions, a pair of supply terminalsadapted to be connected to a source of energizing current, andconnecting means connecting said operating portions to said load circuitbetween said supply terminals for the selective operative energizationof said operating portions in accordance with the conductivity of saidload circuit, whereby said contact means is operative to assume saidfirst, second, or third position accordingly as said oscillator circuitoscillates at said maxi-' mum, intermediate, or minimum amplitude,respectively.

2. Apparatus as specified in claim 1, wherein said contact meansincludes safe-failure contact elements, wherein said relay device isoperative to actuate said contact elements upon the failure of thesource of current to energize the apparatus, wherein said contact meanshas a fourth operating position, and wherein the actuation of saidcontact elements upon the occurrence of said failure is operative tocause said contact means to assume said fourth position.

3. Apparatus as specified in claim 1, wherein each of said operatingportions is a respective relay winding, wherein said connecting meansincludes conductors connecting said relay windings and said load circuitin series between said terminals, wherein said contact means isoperative to assume said first, second, or third operating position,respectively, accordingly as neither, only one, or both of said windingsis operatively energized, wherein said one of said windings is operativeto be operatively energized by a value of the conductivity of said loadcircuit which is insuiiicient to eifect the operative energization ofthe other of said windings, the last mentioned value being thatcorresponding to oscillation of said oscillator circuit at saidintermediate amplitude, and wherein the value of the conductivity ofsaid load circuit corresponding to said maximum amplitude of oscillationis insufficient to effect the operative energization of either of saidwindings while the value of the conductivity of said load circuitcorresponding to said minimum amplitude of oscillation is sufiicient toeffect the operative energization of both of said windings.

4. Apparatus as specified in claim 3, wherein said contact meansincludes a first switch associated exclusively with said one relaywinding and includes a second switch associated exclusively with saidother relay winding, wherein said first switch is operative to establishonly a first connection when said one winding is not operativelyenergized and to establish only a second connection when said onewinding is operatively energized, wherein said second switch isoperative to establish only a third connection when said other windingis not operatively energized and to establish only a fourth connectionwhen said other winding is operatively energized, and wherein thesimultaneous establishment of said first and third connections, saidsecond and third connections, and said second and fourth connectionsconstitutes said first, second, and third operating positions of saidcontact means, respectively.

5. Apparatus as specified in claim 3, wherein said relay device is asingle relay including said 12 two relay windings, wherein said contactmeans includes a switch operative to establish only a first connectionwhen neither of said windings is operatively energized, operative toestablish said first and a second connection simultaneously when onlysaid one winding is operatively energized,. and operative to establishsaid first, said second, and a third connection simultaneously when bothof said windings are operatively energized, and wherein theestablishment of said first connection, the simultaneous establishmentof said first and second connections, and the simultaneous establishmentof said first, second, and third connections constitutes said first,second, and third operating positions of said contact means,respectively.

6. Apparatus as specified in claim 5, wherein said contact means has afourth operating position, wherein said fourth position comprises theinterruption of said first connection, and wherein said relay device isoperative to cause said switch to interrupt said first connection uponfailure of the source of current ,to energize the apparatus.

7. Apparatus as specified in claim 1, wherein each of said operatingportions is a respective relay winding, wherein said connecting meansincludes a second electronic valve having a control electrode includedin a control circuit, having an output electrode included in a secondload circuit, and having a common electrode common to said control andsaid second load circuits, conductors connecting one of said windingsand the first mentioned load circuit in series between said terminals,conductors connecting said control circuit across said one winding andoperation to cause an increase in the conductivity of said first loadcircuit to effect a corresponding decrease in the conductivity of saidsecond load circuit, and conductors connecting the other of saidwindings and said second load circuit in series between said terminals,wherein said contact means is operative to assume said first, second, orthird operating position, respectively, accordingly as only said other,neither, or only said one of said windings is operatively energized,wherein the value of the conductivity of said first mentioned loadcircuit corresponding to said maximum amplitude of oscillation isinsuiiicient to eifect the operative energization of said one windingand is insufiicient to decrease the conductivity of said second loadcircuit and prevent the operative energization of said other winding,and wherein the value of the conductivity of said first mentioned loadcircuit corresponding to said intermediate amplitude of oscillation isinsuflicient to effect the operative energization of said one windingbut is sufficient to decrease the conductivity of said second loadcircuit and prevent the operative energization of said other windingwhile the value of the conductivity of said first mentioned load circuitcorresponding to said minimum amplitude of oscillation is sufficient toeffect the operative energization of said one, winding and to decreasethe conductivity of said second load circuit and prevent the operativeenergization of said other winding.

8. Apparatus as specified in claim '7, wherein said contact meansincludes a first switch associated exclusively with said one relaywinding and includes a second switch associated exclusively with saidother relay winding, wherein said first switch isv operative toestablish only a first connection when said one winding is notoperatively energized and to establish only a second connection whensaid one winding is operatively energized, wherein said second switch isoperative to establish only a third connection when said other windingis not operatively energized and to establish only a fourth connectionwhen said other winding is operatively energized, wherein thesimultaneous establishment of said first and fourth connections, saidfirst and third connections, and said second and third connectionsconstitutes said first, second, and third operative positions of saidcontact means, respectively, and wherein the connection of said controlcircuit across said one winding includes a source of potential tendingto increase the conductivity of said second load circuit.

9. Apparatus as specified in claim 7, wherein said contact meansincludes a first switch associated exclusively with said one relaywinding and includes a second switch associated exclusively with saidother relay winding, wherein said first switch is operative to establishonly a first connection when said one winding is not operativelyenergized and to establish only a second connection when said winding isoperatively energized, wherein said second switch is operative toestablish only a third connection when said other winding is notoperatively energized and to establish only a fourth connection whensaid other winding is operatively energized, wherein 14 the simultaneousestablishment of said first and fourth connections, said first and thirdconnections, and said second and third connections constitutes saidfirst, second, and third operating positions of said contact means,respectively, and wherein said control circuit is connected directlyacross said one winding and is affected solely by the potential dropacross said one winding.

WILLIAM H. WANNAMAKER, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Feb. 14. 1950

